Field of the Disclosure
This disclosure relates to a pneumatic actuator with a diaphragm used in conjunction with a piston having an extended lip. More particularly, this disclosure relates to a pneumatic actuator with a piston having a flange with an extended lip curved around the diaphragm so an edge of the piston flange will not contact the diaphragm during actuator movement.
Description of Related Art
Advantages of turbocharging include increased power output, lower fuel consumption and reduced pollutant emissions. The turbocharging of engines is no longer primarily seen from a high-power performance perspective, but is rather viewed as a means of reducing fuel consumption and environmental pollution on account of lower carbon dioxide (CO2) emissions. Currently, a primary reason for turbocharging is using exhaust gas energy to reduce fuel consumption and emissions. In turbocharged engines, combustion air is pre-compressed before being supplied to the engine. The engine aspirates the same volume of air-fuel mixture as a naturally aspirated engine, but due to the higher pressure, thus higher density, more air and fuel mass is supplied into a combustion chamber in a controlled manner. Consequently, more fuel can be burned, so that the engine's power output increases relative to the speed and swept volume.
In exhaust gas turbocharging, some of the exhaust gas energy, which would normally be wasted, is used to drive a turbine. The turbine includes a turbine wheel that is mounted on a rotatable shaft and is rotatably driven by exhaust gas flow. The turbocharger returns some of this normally wasted exhaust gas energy back into the engine, contributing to the engine's efficiency and saving fuel. A compressor, which is driven by the turbine, draws in filtered ambient air, compresses it, and then supplies it to the engine. The compressor includes a compressor impeller that is mounted on the same rotatable shaft so that rotation of the turbine wheel causes rotation of the compressor impeller.
Turbochargers typically include a turbine housing connected to the engine's exhaust manifold, a compressor housing connected to the engine's intake manifold, and a bearing housing coupling the turbine and compressor housings together. The bearing housing encloses and supports the rotatable shaft.
Turbocharger systems often use pneumatic actuators 12 with a piston 14 and a diaphragm 16. FIG. 1 as detailed below shows an actuator 12 adapted for use with a turbocharger.
The life expectancies for pneumatic actuators for turbochargers are increasing due to increasingly stringent emissions regulations and the new customer control strategies used to meet these regulations. The life of a pneumatic actuator 12 is typically reliant on the life of its diaphragm 16. A common failure includes a radial tear in the valley 46 of the diaphragm 16 due to stress. The piston 14 often causes high stress in this area, which can be due a lack of support in this area as compared with other area of the diaphragm 16.
FIG. 1 shows a prior art pneumatic actuator 12 with a piston 14 and a diaphragm 16 adapted for use with a commercial diesel turbocharger. An actuator rod 18 moves a rod end 20, which connects to a turbocharger component to control its operation. A lower canister 22 and upper canister 24 may house a spring 26, the piston 14, and the diaphragm 16. Other components may include a heat shield 28 around the canisters 22 and 24, and actuator bracket 30 and stud plate 32 at an end with corresponding nuts 34 and studs 36. A bushing 38 and O-ring 40 for sealing are also shown. A hose barb 42 can extend from the upper canister 24 opposite the actuator rod 18.
The flange 44 of the piston 14 may be completely spaced away from the valley 46 of the diaphragm 16 as in FIG. 1. But often the design of the piston 14 is such that a flange 44 at an end of the piston 14 is in contact with the diaphragm 16 of the actuator 12 when the actuator 12 is in its natural or preloaded position as shown in FIG. 2. This design reduces stress in the valley 46 of the diaphragm 16, which is a typical area of failure.
When the piston 14 is in direct contact with the diaphragm 16, it must be free of burrs or sharp edges that can damage the diaphragm 16. Standard piston designs where the flange 44 is in contact with the diaphragm 16 can cause a circumferential tear in the valley 46 of the diaphragm 16 causing diaphragm failure.
Extending the skirt of the piston 14 away from the diaphragm 16 can help eliminate this failure mode. This one step increases the durability of the diaphragm 16 and thus the actuator 12. However, failures can still result from radial tears from stress, rather than circumferential tears. For example, an actuator having a piston that included simple skirt extension resulted in increased the stress in the valley 46 of the diaphragm 16 due to the removal of the diaphragm support provided by the flange 44 of the piston 14.